Well, bear in mind I’m currently in southern Sweden after a hard day’s drive from Germany.
Import the file: import(“filename.stl”);
Render. Curse because it doesn’t appear. Coordinates in an STL file are absolute, and some people provide objects which are thousands of units away from the origin. I don’t know why.
If you have a text-mode file viewer, looking at the first few lines of the file will show you some x/y/z coordinates, so change the signs and put them in a translate. So your OpenSCAD file now looks something like
and it should render somewhere near the origin. I then fine-tune the numbers to get the thing centred.
Then if you want to cut away a section of it, wrap it in a subtract() (which is A-B, boolean AND NOT) or intersect() (which is “only both A and B”, boolean AND). So you might have
and then adjust the size of the cube (and possibly translate it too) until it’s getting the bit you want. Putting a % at the start of the line with the cube will show it in pink (IIRC) so that you can see where it’ll meet the original object.
Some STL files just won’t work - they throw errors when you try to export. Then it’s usually Blender time, though a few don’t work even there.
Hope this helps.